Publication
Analysis of the 2021 Semangko Bay Earthquake Sequence in Southern Sumatra, Indonesia, Using Broadband Seismic Network Data
Publisher:
Seismological Society of America (SSA)
Date:
09-02-2022
DOI:
10.1785/0220210304
Abstract: Beginning on 30 June 2021, hundreds of earthquakes were detected beneath Semangko Bay in southernmost Sumatra, which is located adjacent to the Sunda Strait, a narrow sea passage that separates the islands of Java and Sumatra. A number of these earthquakes were large enough to be felt by people living in the city of L ung, some 100 km to the east. In terms of magnitude and temporal distribution, the earthquakes did not follow a typical mainshock–aftershock sequence because the onset was marked by a cluster of five earthquakes with local magnitudes that ranged between 4.2 and 4.6, followed by a rapid decay in the number of detected events. We have relocated 254 of the 258 earthquakes that were recorded between 30 June and 14 July 2021, with a local magnitude range between ML 0.9 and 4.6, using the double-difference relocation method (hypoDD) focal mechanisms were also determined for a subset of events with a magnitude & . Our results show that the seismicity pattern and focal mechanism solutions are more consistent with a multiple event episode caused by the rupture of several antithetic faults that have a similar strike to the west Semangko fault in southernmost Sumatra rather than a single fault plane. These faults appear to be part of a small graben system located beneath Semangko Bay, which was likely activated by ongoing extension in the Sunda Strait.